Delivery catheter systems and methods

ABSTRACT

Disclosed herein is a delivery catheter for implanting a leadless biostimulator. The delivery catheter includes a shaft and a tubular body having a lumen and an atraumatic end. The atraumatic end includes at least one of a braided, woven or mesh construction configured to facilitate the atraumatic end changing diameter. When a distal portion of the shaft is coupled to a proximal region of the leadless biostimulator, at least one of distally displacing the tubular body relative to the shaft or proximally displacing the shaft relative to the tubular body causes the leadless biostimulator to be received in the volume of the atraumatic end and the atraumatic end to encompass the leadless biostimulator. Conversely, at least one of proximally displacing the tubular body relative to the shaft or distally displacing the shaft relative to the tubular body causes the leadless biostimulator to exit the volume of the atraumatic end.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

FIELD OF THE INVENTION

The present disclosure relates to leadless cardiac pacemakers, and moreparticularly, to features and methods by which they are affixed withinthe heart. More specifically, the present disclosure relates to featuresand methods for delivering a leadless cardiac pacemaker to tissue.

BACKGROUND OF THE INVENTION

Cardiac pacing by an artificial pacemaker provides an electricalstimulation of the heart when its own natural pacemaker and/orconduction system fails to provide synchronized atrial and ventricularcontractions at rates and intervals sufficient for a patient's health.Such antibradycardial pacing provides relief from symptoms and even lifesupport for hundreds of thousands of patients. Cardiac pacing may alsoprovide electrical overdrive stimulation to suppress or converttachyarrhythmias, again supplying relief from symptoms and preventing orterminating arrhythmias that could lead to sudden cardiac death.

Cardiac pacing by currently available or conventional pacemakers isusually performed by a pulse generator implanted subcutaneously orsub-muscularly in or near a patient's pectoral region. Pulse generatorparameters are usually interrogated and modified by a programming deviceoutside the body, via a loosely-coupled transformer with one inductancewithin the body and another outside, or via electromagnetic radiationwith one antenna within the body and another outside. The generatorusually connects to the proximal end of one or more implanted leads, thedistal end of which contains one or more electrodes for positioningadjacent to the inside or outside wall of a cardiac chamber. The leadshave an insulated electrical conductor or conductors for connecting thepulse generator to electrodes in the heart. Such electrode leadstypically have lengths of 50 to 70 centimeters.

Although more than one hundred thousand conventional cardiac pacingsystems are implanted annually, various well-known difficulties exist,of which a few will be cited. For example, a pulse generator, whenlocated subcutaneously, presents a bulge in the skin that patients canfind unsightly, unpleasant, or irritating, and which patients cansubconsciously or obsessively manipulate or “twiddle”. Even withoutpersistent manipulation, subcutaneous pulse generators can exhibiterosion, extrusion, infection, and disconnection, insulation damage, orconductor breakage at the wire leads. Although sub-muscular or abdominalplacement can address some concerns, such placement involves a moredifficult surgical procedure for implantation and adjustment, which canprolong patient recovery.

A conventional pulse generator, whether pectoral or abdominal, has aninterface for connection to and disconnection from the electrode leadsthat carry signals to and from the heart. Usually at least one maleconnector molding has at least one terminal pin at the proximal end ofthe electrode lead. The male connector mates with a corresponding femaleconnector molding and terminal block within the connector molding at thepulse generator. Usually a setscrew is threaded in at least one terminalblock per electrode lead to secure the connection electrically andmechanically. One or more O-rings usually are also supplied to helpmaintain electrical isolation between the connector moldings. A setscrewcap or slotted cover is typically included to provide electricalinsulation of the setscrew. This briefly described complex connectionbetween connectors and leads provides multiple opportunities formalfunction.

Other problematic aspects of conventional pacemakers relate to theseparately implanted pulse generator and the pacing leads. By way ofanother example, the pacing leads, in particular, can become a site ofinfection and morbidity. Many of the issues associated with conventionalpacemakers are resolved by the development of a self-contained andself-sustainable pacemaker, or so-called leadless pacemaker, asdescribed in the related applications cited above.

Self-contained or leadless pacemakers or other biostimulators aretypically fixed to an intracardial implant site by an active engagementmechanism such as a screw or helical member that screws into themyocardium. Despite the numerous advantages provided by leadlesspacemakers, there are challenges that need to be addressed with respectto the delivery systems and methods employed with leadless pacemakers.

BRIEF SUMMARY OF THE INVENTION

Disclosed herein is a delivery catheter for implanting a leadlessbiostimulator including a proximal region, a distal region and anexterior surface extending between the proximal and distal regions. Inone embodiment, the delivery catheter includes a tubular body, anatraumatic end, and a shaft. The tubular body includes a proximal end, adistal end, and a lumen extending through the tubular body between theproximal and distal ends. The atraumatic end is coupled to, and distallyextends from, the distal end. The atraumatic end includes at least oneof a braided, woven or mesh construction that defines a volume that iscoaxial with the lumen and distally terminates as a distal opening inthe atraumatic end. The volume of the braided construction may besubstantially cylindrical and defined by the interior cylindrical wallsurface of the braided construction and extends generally the length ofthe braided construction. The shaft extends through the lumen. The shaftincludes a proximal portion and a distal portion opposite the proximalportion. The shaft and the tubular body are longitudinally displaceablerelative to each other. When the distal portion of the shaft isreleasably coupled to the proximal region of the leadless biostimulator,at least one of distally displacing the tubular body relative to theshaft or proximally displacing the shaft relative to the tubular bodycauses the leadless biostimulator to be received in the volume of thebraided construction via the distal opening and the atraumatic end toexpand and encompass the leadless biostimulator. Conversely, at leastone of proximally displacing the tubular body relative to the shaft ordistally displacing the shaft relative to the tubular body causes theleadless biostimulator to exit the volume of the braided constructionvia the distal opening and the atraumatic end to self-bias into areduced diameter.

Alternatively, in one embodiment, the atraumatic end has an internaldiameter that is substantially the same size as the outer diameter ofthe leadless biostimulator when the atraumatic end is in a neutral statesuch that the leadless biostimulator can be received in and removed fromthe volume of the braided construction without causing any significantchange to the diameter of the atraumatic end. The braided constructionhas sufficient shape memory characteristics to cause the atraumatic endto resume its neutral state when the atraumatic end is compressed into areduced diameter in order to pass through an introducer.

The shaft may extend through the volume of the braided construction. Inone embodiment, the atraumatic end being forced against the exteriorsurface of the biostimulator causes the atraumatic end to expand.

The atraumatic end may include a dual-wall construction. In oneembodiment, the dual-wall construction is a result of a tubular braid,weave, or mesh rolled or folded back on itself, a resulting fold of thedual-wall construction defining a leading distal edge of the atraumaticend that defines the distal opening of the atraumatic end. The leadingdistal edge may have a bullnose longitudinal cross section. The leadingdistal edge may define at least a portion of a funnel configuration ofthe distal opening of the atraumatic end.

The dual-wall construction may support a liner or seal layer. The lineror seal layer may be located between an outer wall and an inner wall ofthe dual-wall construction.

The dual-wall construction may include an inner wall, an outer wall, anda wire reinforcement located between the inner and outer walls. The wirereinforcement may include at least one of longitudinally extendingwires, radially extending wire rings, or a lattice of longitudinallyextending wires and radially extending wire rings. The dual-wallconstruction may include an inner wall, an outer wall, and a reinforcingring located between the inner and outer walls near the leading distaledge of the atraumatic end.

Also disclosed herein is another delivery catheter for implanting aleadless biostimulator including a proximal region, a distal region andan exterior surface extending between the proximal and distal regions.In one embodiment, the delivery catheter includes a tubular body, anatraumatic end, and a shaft. The tubular body includes a proximal end, adistal end, and a lumen extending through the tubular body between theproximal and distal ends. The atraumatic end is coupled to, and distallyextends from, the distal end. The atraumatic end includes an expandabletubular portion including a longitudinally extending fold. Theatraumatic end further includes at least one of a braided, woven or meshconstruction that extends along a leading distal edge of the expandabletubular portion. The expandable tubular portion defines a volume that iscoaxial with the lumen and distally terminates as a distal opening inthe atraumatic end. The volume of the expandable tubular portion may besubstantially cylindrical and defined by the interior cylindrical wallsurface of the expandable tubular portion and extends generally thelength of the expandable tubular portion. The fold and the at least oneof a braided, woven or mesh construction are configured to facilitatethe atraumatic end changing diameter. The shaft extends through thelumen. The shaft includes a proximal portion and a distal portionopposite the proximal portion. The shaft and the tubular body arelongitudinally displaceable relative to each other. When the distalportion of the shaft is releasably coupled to the proximal region of theleadless biostimulator, at least one of distally displacing the tubularbody relative to the shaft or proximally displacing the shaft relativeto the tubular body causes the leadless biostimulator to be received inthe volume of the expandable tubular portion via the distal opening andthe atraumatic end to expand and encompass the leadless biostimulator.Conversely, at least one of proximally displacing the tubular bodyrelative to the shaft or distally displacing the shaft relative to thetubular body causes the leadless biostimulator to exit the volume of theexpandable tubular portion via the distal opening and the atraumatic endto self-bias into a reduced diameter.

Alternatively, in one embodiment, the expandable tubular body isactually a compressible tubular body with an internal diameter that issubstantially the same size as the outer diameter of the leadlessbiostimulator when the atraumatic end is in a neutral state such thatthe leadless biostimulator can be received in and removed from thevolume of the compressible tubular body without causing any significantchange to the diameter of the atraumatic end.

The shaft may also extend through the volume of the compressible orexpandable tubular body, as the case may be. In one embodiment, theatraumatic end being forced against the exterior surface of thebiostimulator causes the atraumatic end to expand.

The at least one of a braided, woven or mesh construction may include adual-wall construction. In one embodiment, the dual-wall construction isa result of a tubular braid, weave, or mesh rolled or folded back onitself. A resulting fold of the dual-wall construction defines a leadingdistal edge of the atraumatic end that defines the distal opening of theatraumatic end.

Also disclosed herein is a method of manufacturing a delivery catheter.In one embodiment, the method includes: manufacturing an atraumatic endof the delivery catheter by folding or rolling a cylindrical wall of atube back on itself to form a dual-wall construction that defines atleast a portion of the atraumatic end, the tube including at least oneof a braided, woven or mesh construction; and securing the atraumaticend to a distal end of a polymer tubular body of the delivery catheter.

In one embodiment of the method, the dual-wall construction includes aninner wall, an outer wall, a cylindrical inner volume defined by theinner wall, a folded end defining a first circular opening of the innervolume, and free ends of the inner and outer walls, the free endsdefining a second circular opening of the inner volume opposite thefirst circular opening.

The method may also include locating a sealing layer or stiffeningstructure between the inner and outer walls of the dual-wallconstruction. A ring structure may be located between the inner andouter walls of the dual-wall construction near the folded end. The ringmay be segmented or discontinuous about its circumferential extent.Conversely, the ring may be non-segmented or continuous about itscircumferential extent. The ring may be radiopaque and visible viafluoroscopy. The ring may be inflatable. The folded end may have afunnel configuration. A polymer may be reflowed about the free ends andthen used to secure the atraumatic end to the tubular body of thedelivery catheter.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the systems and methods disclosed herein are setforth with particularity in the claims that follow. A betterunderstanding of the features and advantages of the systems and methodsdisclosed herein will be obtained by reference to the following detaileddescription that sets forth illustrative embodiments, in which theprinciples of the systems and methods are utilized, and the accompanyingdrawings of which:

FIG. 1 is one embodiment of a delivery system for delivering a leadlesspacemaker.

FIG. 2A is a close-up view of a distal portion of the delivery systemwith an atraumatic end of the delivery system proximal of the leadlesspacemaker.

FIG. 2B is a diagrammatic longitudinal cross section of the leadlesspacemaker and delivery system in the condition illustrated in FIG. 2A.

FIG. 2C is the same view as FIG. 2A, except the atraumatic end of thedelivery system has been distally displaced over the leadless pacemaker.

FIG. 2D is a diagrammatic longitudinal cross section of the leadlesspacemaker and delivery system in the condition illustrated in FIG. 2C.

FIGS. 3A-3B are schematic side and cross-sectional views of a pacemakersheath.

FIG. 3C is a flow chart outlining a method of manufacturing thepacemaker sheath and its joining to a tubular body of the cathetersheath to become part of the catheter sheath.

FIG. 3D is an isometric view of a braided or woven tube used in themanufacture of the pacemaker sheath as outlined in FIG. 3C.

FIGS. 3E-3F are longitudinal cross sections of the tube of FIG. 3Dfolded or rolled back on itself to form a dual-wall construction thatbecomes the pacemaker sheath, as outlined in FIG. 3C.

FIGS. 3G-3H are each an enlarged longitudinal cross section of one ofthe dual-wall constructions of the pacemaker sheath of FIGS. 3E or 3Fshowing optional structures located within the dual-wall construction.

FIG. 3I-3K are the same views as FIGS. 3E-3F, except further along inthe manufacturing process outlined in FIG. 3C.

FIG. 3L is the same view as FIG. 3A, except of another embodiment.

FIG. 3M is a transverse cross section of the pacemaker lead as takenalong section line 3M-3M of FIG. 3L.

FIG. 3N is a longitudinal cross section of an embodiment where the linerlayer is on the exterior of the braided construction.

FIG. 3O is an isometric view of the pacemaker sheath of FIG. 3N.

FIG. 3P is a transverse cross section of the pacemaker sheath as takenalong section line P-P in FIG. 30.

FIGS. 4A-4G are side views of a delivery system attached to a pacemaker.

FIGS. 5A-5D are various views of a catheter handle and tether key.

FIGS. 6A-6B are an alternate embodiment of a delivery system having asingle tether.

DETAILED DESCRIPTION

Various embodiments for delivering system comprising one or moreleadless cardiac pacemakers or biostimulators are described. A leadlesscardiac pacemaker can communicate by conducted communication,representing a substantial departure from conventional pacing systems.For example, an illustrative cardiac pacing system can perform cardiacpacing that has many of the advantages of conventional cardiacpacemakers while extending performance, functionality, and operatingcharacteristics with one or more of several improvements.

In some embodiments of a cardiac pacing system, cardiac pacing isprovided without a pulse generator located in the pectoral region orabdomen, without an electrode-lead separate from the pulse generator,without a communication coil or antenna, and without an additionalrequirement on battery power for transmitted communication.

An embodiment of a cardiac pacing system configured to attain thesecharacteristics comprises a leadless cardiac pacemaker that issubstantially enclosed in a hermetic housing suitable for placement onor attachment to the inside or outside of a cardiac chamber. Thepacemaker can have two or more electrodes located within, on, or nearthe housing, for delivering pacing pulses to muscle of the cardiacchamber and optionally for sensing electrical activity from the muscle,and for bidirectional communication with at least one other devicewithin or outside the body. The housing can contain a primary battery toprovide power for pacing, sensing, and communication, for examplebidirectional communication. The housing can optionally contain circuitsfor sensing cardiac activity from the electrodes. The housing containscircuits for receiving information from at least one other device viathe electrodes and contains circuits for generating pacing pulses fordelivery via the electrodes. The housing can optionally contain circuitsfor transmitting information to at least one other device via theelectrodes and can optionally contain circuits for monitoring devicehealth. The housing contains circuits for controlling these operationsin a predetermined manner.

In some embodiments, a cardiac pacemaker can be adapted for delivery andimplantation into tissue in the human body. In a particular embodiment,a leadless cardiac pacemaker can be adapted for implantation adjacent toheart tissue on the inside or outside wall of a cardiac chamber, usingtwo or more electrodes located on or within the housing of thepacemaker, for pacing the cardiac chamber upon receiving a triggeringsignal from at least one other device within the body.

Self-contained or leadless pacemakers or other biostimulators aretypically fixed to an intracardial implant site by an actively engagingmechanism or primary fixation mechanism such as a screw or helicalmember that screws into the myocardium. Examples of such leadlessbiostimulators are described in the following publications, thedisclosures of which are incorporated by reference: (1) U.S. Pat. No.8,457,742; (2) U.S. application Ser. No. 11/549,581 filed on Oct. 13,2006, entitled “Leadless Cardiac Pacemaker”, and published asUS2007/0088396A1 on Apr. 19, 2007; (3) U.S. application Ser. No.11/549,591, filed on Oct. 13, 2006, entitled “Leadless Cardiac PacemakerSystem with Conductive Communication” and published as US2007/0088397A1on Apr. 19, 2007; (4) U.S. Pat. No. 8,352,025; (5) U.S. Pat. No.7,937,148; (6) U.S. Pat. No. 7,945,333; (7) U.S. Pat. No. 8,010,209; and(8) International Application No. PCT/US2006/040564, filed on Oct. 13,2006, entitled “Leadless Cardiac Pacemaker and System” and published asWO07047681A2 on Apr. 26, 2007.

In addition to the primary fixation mechanism, such as a helix, somebiostimulators may further include a secondary fixation mechanism toprovide another feature for keeping the biostimulator in place withinthe body. Secondary fixation mechanisms can be either active (e.g., thesecondary fixation mechanism can actively engage tissue, either withinor outside the heart), or can be passive (e.g., the secondary fixationmechanism is not attached to tissue but rather prevents thebiostimulator from moving around in the body in the case of accidentaldetachment). Further details on secondary fixation mechanisms can befound in U.S. application Ser. No. 12/698,969.

Leadless pacemakers or biostimulators can be delivered to and retrievedfrom a patient using any of the delivery systems described herein. Insome embodiments, a biostimulator is attached or connected to a deliverysystem and advanced intravenously into the heart. The delivery systemcan include features to engage the biostimulator to allow fixation ofthe biostimulator to tissue. For example, in embodiments where thebiostimulator includes an active engaging mechanism, such as a screw orhelical member, the delivery system can include a docking cap or keyconfigured to engage the biostimulator and apply torque to screw theactive engaging mechanism into the tissue. In other embodiments, thedelivery system includes clips designed to match the shape of a featureon the biostimulator and apply torque to screw the active engagingmechanism into the tissue.

The delivery system can also include atraumatic tip configurations thatcan be extended over the leadless pacemaker and primary fixationmechanism when the leadless pacemaker is being delivered into, orwithdrawn from, the patient. The atraumatic tip configurations can alsobe retracted from about the leadless pacemaker and primary fixationmechanism when the primary fixation mechanism is caused to displacerelative to the heart tissue such as when the primary fixation mechanismin the form of a helix is screwed into or out of the heart tissue at animplantation site.

FIG. 1 illustrates a pacemaker delivery system 100 configured fordelivery of a leadless pacemaker 102 into a patient. Delivery system 100can include a guide catheter sheath 111 including an atraumatic distalend 104 in the form of a pacemaker sheath 104. Delivery system 100 canalso have a pacemaker introducer sheath 107 and a catheter shaft 106.Catheter shaft 106 includes at its proximal end a handle 108, deflectionknob 110, and tether shuttle 112. Each of longitudinal bodies 107, 111,106 includes a flush port 114 a, 114 b, 114 c extending respectivelytherefrom. As can be understood from FIG. 1, catheter shaft 106 extendsthrough guide catheter sheath 111, which extends through introducersheath 107. Each of longitudinal bodies 106, 107, 111 are displaceableproximal-distal relative to each other.

As discussed in greater detail below, atraumatic pacemaker sheath 104may have a braided or woven construction that is sufficiently flexibleto allow atraumatic pacemaker sheath 104 to encompass leadless pacemaker102 or to have a diameter that is smaller than a diameter of leadlesspacemaker 102 when not encompassing leadless pacemaker 102. Thedeflection knob 110 can be used to deflect catheter shaft 106 withincatheter sheath 111 to steer and guide the catheter during implantationand/or removal of the pacemaker. Flush ports 114 a, 114 b, and 114 c canbe used to flush saline or other fluids through the catheter. Atraumaticsheath 104 forms the distal most region of catheter sheath 111. Cathetersheath 111 can be advanced distally over catheter shaft 106 such thatatraumatic sheath 104 is caused to extend over leadless pacemaker 102.Also, the distal displacement of catheter sheath 111 relative tocatheter shaft 106 can be used to provide additional steering andsupport for the delivery catheter during implantation and to surroundthe pacemaker as it is introduced through a trocar or introducer sheath107 into the patient. Catheter sheath 111 can be retracted proximallyover catheter shaft 106 such that atraumatic sheath 104 is caused toretract from over leadless pacemaker 102, the braided construction ofatraumatic sheath 104 being such that atraumatic sheath 104 self-biasesinto a reduced diameter. In one embodiment, the reduced diameter ofatraumatic sheath 104 will be no greater than the diameter of leadlesspacemaker 102.

Alternatively, pacemaker sheath 104 may have a neutral shape it assumesor biases into wherein its internal diameter is the same as the outerdiameter of leadless pacemaker 102 such that the pacemaker sheath canreadily slip over and off of the leadless pacemaker without thepacemaker sheath changing its internal diameter. However, on account ofthe flexibility and shape memory nature of the pacemaker sheath, thepacemaker sheath can be compressed for passage through introducer 107and, once through the introducer, the shape memory nature of thepacemaker sheath causes the pacemaker sheath to assume its neutral shapewith its internal diameter that is the same as the outer diameter of theleadless pacemaker. FIG. 2A is a close-up view of a distal portion ofdelivery system 200 and pacemaker 202, and FIG. 2B is a diagrammaticlongitudinal cross section of the same components in the same condition.The pacemaker 202 of FIGS. 2A and 2B can include a helix 203 forattachment of the pacemaker to tissue. In FIGS. 2A and 2B, the pacemakeris attached to docking cap 218 of catheter shaft 206. Atraumaticpacemaker sheath 204, along with the rest of guide catheter sheath 211,is shown pulled back proximally along catheter shaft 206 to exposepacemaker 202 and helix 203. Thus, when guide catheter sheath 211 ispulled back proximally thereby causing its atraumatic distal end region204 to pull back proximally, as shown in FIGS. 2A and 2B, pacemaker 202is in an exposed, delivery configuration such that helix 203 is exposedfor screwing into or out of heart tissue at a implantation target site.

In FIGS. 2C and 2D, guide catheter sheath 211 is extended distally tocause atraumatic pacemaker sheath 204 to cover catheter shaft 206,pacemaker 202, and helix 203 to protect patient tissue from the sharpedges of helix 203 during implantation. Thus, when catheter sheath 211and its atraumatic distal end region 204 in the form of pacemaker sheath204 are advanced distally to protect the pacemaker and helix, as shownin FIGS. 2C and 2D, the pacemaker 202 and helix 203 are in a protected,advancement configuration.

FIG. 3A is a close-up view of atraumatic distal end region 204 orpacemaker sheath 304 of catheter sheath 311 (shown in FIG. 3K) ofdelivery system 300. FIG. 3B is a transverse cross section of onlypacemaker sheath 304. As shown, pacemaker sheath 304 includes a braided,woven or mesh construction, which is configured to minimize thepotential for the helix to become stuck in the braided, woven or meshconstruction. For example, in one embodiment to minimize the likelihoodof a helix of a common size and configuration becoming stuck in thebraided construction, the braided construction includes 72-144 # wireswith a diameter of between approximately 0.0015 inch and approximately0.006 inch. Other braided constructions may be employed to minimize thehelix becoming stuck in the braided construction where the helix is ofan uncommon size or configuration.

The wires of the braided construction may be made of metal materialssuch as, for example, nickel-titanium alloy (“Nitinol”),cobalt-chromium-nickel alloy (“Elgioly”), 316 stainless steel, 304stainless steel, or etc. In one embodiment, some of the wires (e.g.,one, two, three, four, or more wires) or all of the wires of the braidedconstruction may be of a radiopaque material such as tungsten, platinum,gold, or etc. to facilitate the braided construction being visible viafluoroscopy. In some embodiments, the wires may have a diameter range ofapproximately 0.001 inch to approximately 0.005 inch, and the length ofpacemaker sheath 304 may have a range of approximately 1 cm toapproximately 10 cm with a preferred length range of approximately 5 cmto approximately 7 cm, depending on the length of the leadless pacemakerto be received in the pacemaker sheath. In one embodiment, the braidedconstruction may be woven from polymer materials such as, for example,polyether block amide (“PEBAX”), polyethylene terephthalate (“PET”),polyethylene (“PE”), nylon, urethane, polyester, or a blend of any ofthe aforementioned where appropriate.

In one embodiment, the pacemaker sheath 304 is manufactured and coupledto the rest of the catheter sheath 311 via the following methodology,which is outlined in the flow chart of FIG. 3C. FIG. 3D is an isometricview of a cylindrical braided tube 350 used to manufacture the pacemakersheath, and this tube 350 is provided as part of the manufacturingprocess [block 380 of FIG. 3C]. The braided tube 350 has a cylindricalwall 352 with a woven or braided construction formed of theabove-mentioned wires and materials, the cylindrical wall defining acylindrical interior 353.

FIG. 3E is a longitudinal cross section of cylindrical wall 352 after ithas been folded or rolled back on itself to form a dual-wallconstruction having an inner wall 352 a and an outer wall 352 b [block382 of FIG. 3C]. Each wall 352 a, 352 b has a respective free end 354 a,354 b, and the distal or leading edge 355 of the resulting pacemakersheath 304 is a bullnose or rounded edge 355 resulting from the foldingof cylindrical wall 352 back on itself. Another cylindrical interiorspace 356 is defined by the dual-wall construction.

As illustrated in FIG. 3F, which is the same view as FIG. 3E, exceptwith a different result, in some embodiments, distal leading edge 355 ofpacemaker sheath 304 is flared or funnel shaped to facilitate thepacemaker sheath extending over the leadless pacemaker, as can beunderstood from FIGS. 2A-2B. This flared or funnel shaped edge 355illustrated in FIG. 3F can be heat set to maintain the funnel shape. Inone embodiment, the pacemaker sheath or at least the flared or funnelshaped edge can be dip coated to mitigate any threaded protrusions ofthe braid, thereby reducing the chance of interferences resulting fromsuch protrusions.

In one optional embodiment, the pacemaker sheath 304 can be coated witha hydrophilic, drug or parylene coating to inhibit or prevent thrombus[block 383 of FIG. 3C]. Such coatings are advantageous if the pacemakersheath does not include a liner layer on the outside of the pacemakersheath as described below with respect to block 385 of FIG. 3C.

FIG. 3G is an enlarged longitudinal cross section of one of thedual-wall arrangements of pacemaker sheath 304 of FIGS. 3E or 3F. Asshown in FIG. 3G, in one optional embodiment, a structure or layer 357extends through the dual-wall construction between inner and outer walls352 a, 352 b [block 384 of FIG. 3C]. In one embodiment, the layer 357 isa liner or sealing layer formed of a polymer material such aspolyurethane, PEBAX, nylon, polyester, polyurethane, PTFE, EPTFE, orappropriate blends of these materials such as a polyester-polyurethaneblend. The layer 357 may have a durometer of approximately 25 toapproximately 72 on scale D. The layer 357 may have a thickness ofbetween approximately 0.0001 inch and approximately 0.005 inch. In oneembodiment, liner layer 357 is 0.001 inch thick polyurethane.

In one embodiment that is not explicitly shown in the figures, insteadof liner layer 357 being located between walls 352 a, 352 b, liner layer357 is supported on the dual-wall construction so as to extend along theinner circumferential surface of inner wall 352 a such that the linerlayer defines cylindrical inner volume 356.

In one embodiment the structure 357 is a stiffening structure. In oneembodiment stiffening structure 357 is a plurality of stiffening wiresformed of the same type and size of wire forming the braidedconstruction of sheath 304 as described above. In one embodiment, thestiffening wires may have a diameter range of approximately 0.003 inchand approximately 0.01 inch. The stiffening wires may be in the form ofa plurality of longitudinally extending wires evenly radially dispersedin the space between the inner and outer walls. Alternatively, thestiffening wires may be in the form of a plurality of radial ringsevenly longitudinally dispersed in the space between the inner and outerwalls. In yet another alternative, the plurality of longitudinallyextending wires and plurality of radial rings may be combined to form awire mesh or lattice between the inner and outer walls. Regardless ofhow the stiffening wires are arranged between the inner and outer walls,the stiffening wires increase the column strength of the pacemakersheath.

In one optional embodiment as illustrated in FIG. 3N-3P, instead ofliner layer 357 being located between walls 352 a, 352 b, liner layer357 is supported on the dual-wall construction so as to extend along theouter circumferential surface of outer wall 352 b such that the linerlayer defines the cylindrical outer circumference of pacemaker sheath304 [block 385 of FIG. 3C]. As illustrated in FIG. 3N, the distal end390 of liner layer 357 may be rounded or folded back on itself to beatraumatic in configuration and may be generally flush with distal end355 of the braided construction or may distally overhang distal end 355by approximately 0.0 inch to approximately 0.2 inch. As shown in FIGS.3N and 3O, the distal region of liner layer 357 may be secured to thebraided construction via sutures 392. As illustrated in FIG. 3N, theproximal region of the liner layer may be secured to the braidedconstruction via heat bonded regions 394. In some instances, some or allof the sutures 392 may be of a radiopaque material such asplatinum-iridium alloy, platinum, gold or etc. to facilitate thevisualization of the distal end of the pacemaker sheath underfluoroscopy. The liner layer 357 can distally terminate with edges thatproject distally generally straight or in an outwardly flared or funnelshape.

In some embodiments, liner layer 357 may be supported loosely orunrestrained on the underlying braided construction. In someembodiments, liner layer 357 may be laminated onto the underlyingbraided construction.

As indicated in FIGS. 3O and 3P, liner layer 357 may have a slit, seam,or fold 396 that allows the liner layer to expand and contract with theunderlying braided construction as the pacemaker sleeve 304 moves acrossthe exterior of the leadless pacemaker. By designing pacemaker sheath304 with a slit, seam, or fold 396 in the liner layer that runslongitudinally along the sheath, the cross sectional diameter of thepacemaker sheath can be reduced by folding or overlapping the linerlayer of the pacemaker sheath over itself at eh slit, seam or fold.Conversely, the cross sectional diameter of the pacemaker sheath can beincreased by unfolding or expanding the slit, seam or fold.

FIG. 3H is also an enlarged longitudinal cross section of one of thedual-wall arrangements of pacemaker sheath 304 of FIGS. 3E or 3F. Asshown in FIG. 3H, in one optional embodiment, a ring structure 358radially extends through the dual-wall construction between inner andouter walls 352 a, 352 b near distal leading edge 355 [block 386 of FIG.3C]. In one embodiment, the ring structure 358 is formed of a radiopaquematerial such as platinum, platinum-iridium alloy, gold, barium filledpolymer, tungsten, or etc. to be visible via fluoroscopy. The ring mayhave a thickness of between approximately 0.0005 inch and approximately0.01 inch. Where the ring is barium filled polymer, the ring can be heatbonded to the liner layer 357 where present.

The ring may be segmented or discontinuous about its circumferentialextent. Conversely, the ring may be non-segmented or continuous aboutits circumferential extent. In one embodiment, the ring structure 358may be used to increase the radial strength or rigidity of the distalleading edge. In one embodiment, all the optional elements discussedwith respect to FIGS. 3G and 3H are present in the pacemaker sheath.

FIGS. 3I, 3J and 3K are the same views as FIGS. 3E and 3F, exceptfurther along in the manufacturing process outlined in FIG. 3C. As shownin FIG. 31, a polyring 360 is reflowed about the free ends 354 a, 354 bof walls 352 a, 352 b of pacemaker sheath 304 [block 388 of FIG. 3C]such that the polyring becomes a polyend 362 of the pacemaker sheath, ascan be understood from FIG. 3J. The polyend of pacemaker sheath 304 isthen mated with and reflowed onto, or otherwise connected with, a distalend 364 of a tubular body 366 of catheter sheath 311 [block 390 of FIG.3C], as indicated in FIG. 3K. The resulting catheter sheath may then beassembled with the rest of its components and then combined as completea catheter sheath 111 with introducer sheath 107 and catheter shaft 106to become delivery system 100, as illustrated in FIG. 1.

In an alternative embodiment, instead of employing a braided pacemakersheath as described above with respect to FIGS. 3A-3K, the pacemakersheath only employs a braided atraumatic buffer portion 370 along itsextreme distal edge. For example, as shown in FIGS. 3L and 3M, which arerespectively the same views depicted in FIGS. 3A and 3B, pacemakersheath 304 can include a crease or fold 372 along the length of thepacemaker sheath, and atraumatic braided portion or donut 370 extendsalong the extreme distal edge of pacemaker sheath 304 to provide anatraumatic buffer 370 on the leading extreme distal edge of thepacemaker sheath. The braided donut 370 may be manufactured from theaforementioned materials and via methods similar to those describedabove with respect to the embodiment of FIGS. 3A-3K.

By designing pacemaker sheath 304 with a fold 372 that runslongitudinally along the sheath, the cross sectional diameter of thepacemaker sheath can be reduced by folding the pacemaker sheath overitself. Thus, similar to already described above, during initialimplantation of the pacemaker through a introducer sheath into thepatient, the pacemaker sheath can be positioned just proximal to thepacemaker, and folded along fold 372 so as to have a cross sectionaldiameter close to or equal to the same diameter as the pacemaker. Thisallows a smaller diameter introducer sheath to be used than wouldnormally be necessary, since those delivery systems must incorporate alarger introducer sheath to allow passage of a full sized pacemakersheath. After the delivery system is inserted through the introducersheath into the patient, the sheath can be advanced distally over theleadless pacemaker. Advancing the pacemaker sheath distally over thepacemaker causes fold 372 to unfold, thereby increasing the diameter ofthe pacemaker sheath so that it can slide over and cover the pacemakerand fixation helix. FIG. 3M is a cross sectional view of the pacemakersheath 304 and fold 372 as taken along section line 3M-3M of FIG. 3L,giving another view on how the cross sectional diameter of the pacemakersheath can increase and decrease. Since atraumatic donut 370 extendsalong the leading distal edge of the pacemaker sheath and the pacemakersheath is radially discontinuous on account of its longitudinal fold372, atraumatic donut 370 is also radially discontinuous such that itsfree ends 374 a, 374 b overlap each other as can be understood from FIG.3L and in much the same way as the rest of the pacemaker sheath asdepicted in FIGS. 3L and 3M.

During initial insertion of the delivery system into a patient, aphysician can gain access to the patient's venous system with anintroducer sheath using the Seldinger technique (not shown). Thedelivery system, including the leadless pacemaker, catheter sheath andcatheter shaft, can then be advanced through the introducer sheath intothe patient's venous system to facilitate delivery of the pacemaker intothe heart. Reducing the diameter of the pacemaker, the delivery system,and thus the introducer sheath, provides for easier and less intrusiveaccess to a patient's venous system.

As can be understood from FIGS. 2A-3K, pacemaker sheath 304 has a wovenexpandable configuration that self-biases to a reduced diameter that isat least as small as the diameter of the leadless pacemaker and issufficiently readily expandable by simply distally displacing pacemakersheath 304 against the leadless pacemaker such that sheath 304 expandsabout and envelopes leadless pacemaker. Thus, during initialimplantation of the pacemaker through an introducer sheath into thepatient, the pacemaker sheath can be positioned just proximal to thepacemaker, as illustrated in FIGS. 2A-2B, the diameter of the pacemakersheath self-biasing to its minimum diameter so as to have a crosssectional diameter close to or equal to the same diameter as thepacemaker. This allows a smaller diameter introducer sheath to be usedthan would normally be necessary, since those delivery systems mustincorporate a larger introducer sheath to allow passage of a full sizedpacemaker sheath. After the delivery system is inserted through theintroducer sheath into the patient, the sheath can be advanced distallyover the leadless pacemaker. Advancing the pacemaker sheath distallyover the pacemaker causes the braided or woven expandable configurationof the pacemaker sheath to expand sufficiently with respect to itsdiameter that the pacemaker sheath can slide over and cover thepacemaker and fixation helix, as illustrated in FIGS. 2C-2D, therebypreventing the helix from contacting patient tissue.

It should be noted that while the pacemaker sheath is shown in FIGS. 2Band 2D as having a neutral configuration with an internal diameter thatis less than the outer diameter of the leadless pacemaker, therebyrequiring the pacemaker sheath to expand as it is distally displacedover the leadless pacemaker for the leadless pacemaker to be received inthe internal volume of the pacemaker sheath, in other embodiments, thepacemaker sheath has a neutral configuration with an internal diameterthat is the same as the outer diameter of the leadless pacemaker. Morespecifically, pacemaker sheath 104 may have a neutral shape it assumesor biases into wherein its internal diameter is the same as the outerdiameter of leadless pacemaker 102 such that the pacemaker sheath canreadily slip over and off of the leadless pacemaker without thepacemaker sheath changing its internal diameter. However, on account ofthe flexibility and shape memory nature of the pacemaker sheath, thepacemaker sheath can be compressed for passage through introducer 107and, once through the introducer, the shape memory nature of thepacemaker sheath causes the pacemaker sheath to assume its neutral shapewith its internal diameter that is the same as the outer diameter of theleadless pacemaker.

FIG. 4A illustrates delivery system 400, including pacemaker 402comprising helix 403 and attachment feature 424, and the deliverycatheter comprising the distal region or pacemaker sheath 404 of thecatheter sheath, catheter shaft 406, docking cap 418, and tethers 422 aand 422 b. The tethers can comprise wires, shafts, tubes, cords, ropes,strings, or other similar structures that can extend throughout thecatheter shaft. In some embodiments, the tethers comprise a shape memorymaterial, such as nitinol. In other embodiments, the tethers comprisestainless steel wires or braids. In FIG. 4A, the pacemaker 402 is notattached to docking cap 418 of the delivery catheter. The process ofconnecting the pacemaker to the delivery catheter will now be described.

Referring to FIG. 4B, tethers 422 a and 422 b can include distalfeatures 426 a and 426 b. The distal features can be, for example,features on the tethers that protrude radially from the tether, such asbumps, spheres, cylinders, rectangles, or other similar shapes extendingoutwards from the tethers. In some embodiments, the distal features canbe expandable, such as balloons or expandable mechanical structures.Generally, the distal features have a cross sectional diameter largerthan the cross sectional diameter of the tethers. As shown, in oneembodiment, distal feature 422 a can be advanced further from thecatheter than distal feature 422 b, so that when the tethers are pushedtogether, distal feature 422 b rests against tether 422 a. This causesthe combined cross sectional diameter of both distal features andtethers to be less than if the distal features were lined up side byside. By way of comparison, in FIG. 4C the distal features 426 a and 426b are lined up side by side and therefore have a greater combined crosssectional diameter when pressed together than is shown in FIG. 4B.

To connect the delivery catheter to the pacemaker, the length of tethers422 a and 422 b, and thus the position of distal features 426 a and 426b, can be adjusted so that distal features 426 a and 426 b are notaligned in a side by side configuration (e.g., the un-alignedconfiguration shown in FIGS. 4A-4B). When the tethers and distalfeatures are in this un-aligned configuration, the cross sectionaldiameter of the distal features is reduced since the distal features arenot positioned side by side. The tether distal features 426 a and 426 bcan then be advanced in this un-aligned configuration through hole 428of attachment feature 424, as shown in FIGS. 4D-4F. In this embodiment,the diameter of hole 428 should be sufficiently large enough to allowthe distal features 426 a and 426 b of tethers 422 a and 422 b to passwhen in the un-aligned configuration. Upon passing the distal featuresthrough the hole 428, the length of the tethers can then be adjusted toalign the distal features in the side by side configuration (e.g., asshown in FIGS. 4C and 4E). When the distal features are positioned sideby side, the combined cross sectional diameter of the distal featuresbecomes larger than the diameter of hole 428, which essentially locksthe tethers and distal features in the attachment feature 424 bypreventing the distal features from being able to pass proximallythrough the hole 428.

Still referring to FIGS. 4C and 4D, the docking cap 418, which issupported on the distal end catheter shaft 406 of the delivery catheter,can include a torque slot 430 (shown in FIG. 4C) sized and configured tomate with a torque key 432 (shown in FIG. 4D) disposed on a proximal endof the pacemaker. The torque slot 430 is located in docking cap 418 andcoupled to a torque shaft 431, which runs the length of catheter shaft406 of the delivery catheter to extend into the handle (not shown). InFIGS. 4C and 4D, torque key 432 is shown as a “male” key on the proximalend of pacemaker 402, and torque slot 430 is shown as a “female” key,but it should be understood that in other embodiments, the “male” keycan be located on the attachment feature 418, and the “female” key canbe disposed on the pacemaker. It should also be appreciated that key 432and slot 430 can comprise any number of shapes, such as square,rectangle, triangle, pentagon, hexagon, cross, “X”, etc., so long as key432 fits within torque slot 430 for the transfer of rotation torquebetween the two elements 430, 432. Once the tethers are locked withinthe attachment feature, the tethers can be pulled proximally to pullattachment feature 424 and the pacemaker towards the catheter and toattach the pacemaker to the delivery catheter, thereby engaging torqueslot 430 with torque key 432 (as shown in FIG. 4G).

FIGS. 5A-5D are close-up views of handle 508 of delivery system 500. InFIG. 5A, handle 508 includes deflection knob 510, tether shuttle 512,tether adjustment feature 516, and flush port 514 c. As described above,deflection knob 510 provides for steering and guidance of the catheterduring implantation and/or removal of the pacemaker. The flush port 514c can be used to flush saline or other fluids through the catheter.Referring now to FIGS. 5B and 5C, tether adjustment feature 516 can beconfigured to adjust the length of tethers 522 a and 522 b that extendsdistally outwards from the delivery catheter, causing the distalfeatures (not shown) to be in either a side by side “locked”configuration or an un-aligned “unlocked” configuration.

The tether adjustment feature can comprise an Allen wrench or any othersuitable key, and can be configured to mate with and engage proximalkeys 534 a and 534 b of tethers 522 a and 522 b, respectively, which aredisposed within shuttle 512. In another embodiment, the tetheradjustment feature can comprise knobs or dials on the handle itself, anda user can simply turn the knobs or dials to adjust the length of thetethers. The shuttle can be inserted into handle 508, as shown in FIG.5D. The proximal keys 534 a and 534 b of tethers 522 a and 522 b areshown without shuttle 536 in FIG. 5C for ease of illustration. Rotationof tether adjustment feature 516 causes proximal keys 534 a and/or 534 bto move distally or proximally within shuttle 512, which thereforechanges the length of tethers 522 a and/or 522 b extending distally fromthe delivery catheter. Thus, the tether key can be used to either alignthe distal features of the tethers in a side by side (e.g., locked)configuration, or alternatively, to place the distal features of thetethers in an un-aligned (e.g., unlocked configuration), permittingdocking and locking of the pacemaker to the delivery catheter.

Referring back to FIGS. 4D-4G and 5A, it can now be understood how thepacemakers described herein can be delivered and attached to tissue, andthen released from the delivery system. In FIGS. 4D-4F, tethers 422 aand 422 b can be inserted in an “unlocked” or un-aligned configurationinto hole 428 of attachment feature 424. The distal features of thetethers can then be aligned so as to lock the distal features in theattachment feature. Referring to FIG. 5A, tether shuttle 512 can then bepulled proximally to cause the tethers to move proximally, therebydocking the pacemaker against the delivery catheter (as shown in FIG.4G). When the pacemaker is docked against the delivery catheter, torquekey 432 of the pacemaker (shown in Fig.4D) fits within and is mated totorque slot 430 of the delivery catheter (shown in FIG. 4C).

Referring to FIG. 5A, tether shuttle 512 of handle 508 can then berotated, which rotates torque shaft 431 (shown in FIG. 4C) within thedelivery catheter and applies torque to torque slot 430, and thus totorque key 432 on the pacemaker. By rotating the shuttle, and thus thetorque shaft, the delivery catheter applies torque to the pacemaker toscrew the fixation helix of the pacemaker into tissue. Once the fixationhelix is fully inserted into tissue, the tethers can be placed into anun-aligned or “unlocked” configuration with tether adjustment feature516, allowing the tethers and distal features to be removed from theattachment feature of the pacemaker. Once the delivery catheter isdisengaged from the pacemaker, the catheter can be removed from thepatient, leaving the pacemaker in place at the target tissue.

FIGS. 6A and 6B illustrate an alternate embodiment for attaching adelivery catheter to a pacemaker. The embodiment shown in FIGS. 6A and6B employs a similar concept to that described above. However, insteadof using two tethers, as described above, the embodiment of FIGS. 6A and6B utilizes a single tether 622, having both a distal feature 626 a anda proximal feature 626 b. In the embodiment of FIGS. 6A and 6B, thetether 622 can comprise a shape memory alloy, such as nitinol, and caninclude a pre-bent or pre-biased shape. This pre-biased shape can allowthe distal feature 626 a of the tether to naturally bias outwards, asshown in FIG. 6A.

To attach the pacemaker 602 to the delivery catheter, as shown in FIG.6A, the distal feature 626 a of tether 622 can be threaded throughattachment feature 624 of pacemaker 602. Once the tether is threadedthrough the attachment feature, the tether can be folded back againstitself, so that distal feature 626 a is adjacent to, but not directlybeside proximal feature 626 b. The distal and proximal features shouldbe aligned in an un-aligned or “unlocked” configuration, as describedabove in the two-tether embodiments. This configuration allows thedistal and proximal features to be inserted into hole 628 of docking cap618, as shown in FIG. 6B. Once the distal and proximal features areadvanced past the hole 628, an interior chamber (not shown) in thecatheter opens up to a diameter larger than the diameter of the hole628. This interior chamber has a diameter large enough to accommodateboth the distal and proximal features in a side by side or “locked”configuration. Thus, the length of the tether can be adjusted to alignthe distal and proximal features in the side by side configuration,causing the combined cross sectional diameter of the distal and proximalfeatures to be larger than the diameter of hole 628. The result is thelocking of tether 622 within the delivery catheter.

Other features of the embodiment of FIGS. 6A-6B can be the same asdescribed above, such as the torque keys, slots, and shafts that allowthe delivery catheter to apply rotational torque to the pacemaker toscrew it into tissue. Further, atraumatic pacemaker sheath 604 can be asdescribed above to facilitate the safe delivery of leadless pacemaker602 to the implantation site.

As for additional details pertinent to the present disclosure, materialsand manufacturing techniques may be employed as within the level ofthose with skill in the relevant art. The same may hold true withrespect to method-based aspects of the present disclosure in terms ofadditional acts commonly or logically employed. Also, it is contemplatedthat any optional feature of the systems and methods disclosure hereinmay be set forth and claimed independently, or in combination with anyone or more of the features described herein. Likewise, reference to asingular item, includes the possibility that there are plural of thesame items present. More specifically, as used herein and in theappended claims, the singular forms “a,” “and,” “said,” and “the”include plural referents unless the context clearly dictates otherwise.It is further noted that the claims may be drafted to exclude anyoptional element. As such, this statement is intended to serve asantecedent basis for use of such exclusive terminology as “solely,”“only” and the like in connection with the recitation of claim elements,or use of a “negative” limitation. Unless defined otherwise herein, alltechnical and scientific terms used herein have the same meaning ascommonly understood by one of ordinary skill in the art to which thispresent disclosure belongs. The breadth of the present disclosure is notto be limited by the subject specification, but rather only by the plainmeaning of the claim terms employed.

What is claimed is:
 1. A delivery catheter for implanting a leadlessbiostimulator including a proximal region, a distal region and anexterior surface extending between the proximal and distal regions, thedelivery catheter comprising: a tubular body including a proximal end, adistal end, and a lumen extending through the tubular body between theproximal and distal ends; an atraumatic end coupled to, and distallyextending from, the distal end, the atraumatic end including at leastone of a braided, woven or mesh construction that defines a volume ofthe atraumatic end that is coaxial with the lumen and distallyterminates as a distal opening in the atraumatic end, the at least oneof a braided, woven or mesh construction being configured to facilitatethe atraumatic end changing diameter; and a shaft extending through thelumen, the shaft including a proximal portion and a distal portionopposite the proximal portion, the shaft and the tubular body beinglongitudinally displaceable relative to each other, wherein, when thedistal portion of the shaft is releasably coupled to the proximal regionof the leadless biostimulator, at least one of distally displacing thetubular body relative to the shaft or proximally displacing the shaftrelative to the tubular body causes the leadless biostimulator to bereceived in the volume of the atraumatic end via the distal opening andthe atraumatic end to encompass the leadless biostimulator, and at leastone of proximally displacing the tubular body relative to the shaft ordistally displacing the shaft relative to the tubular body causes theleadless biostimulator to exit the volume of the atraumatic end via thedistal opening.
 2. The delivery catheter of claim 1, wherein theatraumatic end is configured to expand when the leadless biostimulatoris received in the volume of the atraumatic end via the distal opening.3. The delivery catheter of claim 1, wherein the atraumatic end isconfigured to self-bias into a reduced diameter when the leadlessbiostimulator exits the volume of the atraumatic end via the distalopening.
 4. The delivery catheter of claim 1, wherein the atraumatic endhas an internal diameter that is substantially the same size as an outerdiameter of the leadless biostimulator when the atraumatic end is in aneutral state such that the leadless biostimulator can be received inand removed from the volume of the braided construction without causingany significant change to the diameter of the atraumatic end.
 5. Thedelivery catheter of claim 4, wherein the braided, mesh or wovenconstruction has sufficient shape memory characteristics to cause theatraumatic end to resume its neutral state when the atraumatic end iscompressed into a reduced diameter in order to pass through anintroducer.
 6. The delivery catheter of claim 1, wherein the shaft alsois configured to extend through the volume of the atraumatic end.
 7. Thedelivery catheter of claim 1, wherein the atraumatic end is configuredto expand when the atraumatic end is forced against the exterior surfaceof the biostimulator.
 8. The delivery catheter of claim 1, wherein theatraumatic end includes a dual-wall construction.
 9. The deliverycatheter of claim 8, wherein the dual-wall construction is a result of atubular braid, weave, or mesh rolled or folded back on itself, aresulting fold of the dual-wall construction defining a leading distaledge of the atraumatic end that defines the distal opening of theatraumatic end.
 10. The delivery catheter of claim 9, wherein theleading distal edge has a bullnose or straight longitudinal crosssection.
 11. The delivery catheter of claim 9, wherein the leadingdistal edge defines at least a portion of a flared or funnelconfiguration of the distal opening of the atraumatic end.
 12. Thedelivery catheter of claim 9, wherein the dual-wall constructionsupports a liner or seal layer.
 13. The delivery catheter of claim 12,wherein the liner or seal layer is located between an outer wall and aninner wall of the dual-wall construction.
 14. The delivery catheter ofclaim 12, wherein the liner or seal layer is extends about the exteriorof the outer wall of the dual-wall construction.
 15. The deliverycatheter of claim 9, wherein the dual-wall construction includes aninner wall, an outer wall, and a wire reinforcement located between theinner and outer walls, the wire reinforcement including at least one oflongitudinally extending wires, radially extending wire rings, or alattice of longitudinally extending wires and radially extending wirerings.
 16. The delivery catheter of claim 9, wherein the dual-wallconstruction includes an inner wall, an outer wall, and a radiopaquering located between the inner and outer walls near the leading distaledge of the atraumatic end.
 17. The delivery catheter of claim 16,wherein the radiopaque ring is segmented or discontinuous.
 18. Thedelivery catheter of claim 1, wherein the at least one of a braided,woven or mesh construction includes 72-144 # wires with a diameter ofbetween approximately 0.0015 inch and approximately 0.006 inch.
 19. Thedelivery catheter of claim 1, wherein the at least one of a braided,woven or mesh construction includes at least one of nickel-titaniumalloy, cobalt-chromium-nickel alloy, 316 stainless steel, 304 stainlesssteel, polyether block amide, polyethylene terephthalate, polyethylene,nylon, urethane, or polyester.
 20. A delivery catheter for implanting aleadless biostimulator including a proximal region, a distal region andan exterior surface extending between the proximal and distal regions,the delivery catheter comprising: a tubular body including a proximalend, a distal end, and a lumen extending through the tubular bodybetween the proximal and distal ends; an atraumatic end coupled to, anddistally extending from, the distal end, the atraumatic end including atubular portion including a longitudinally extending fold, theatraumatic end further including at least one of a braided, woven ormesh construction that extends along a leading distal edge of thetubular portion, the tubular portion defining a volume of the atraumaticend that is coaxial with the lumen and distally terminates as a distalopening in the atraumatic end, the fold and the at least one of abraided, woven or mesh construction being configured to facilitate theatraumatic end changing diameter; and a shaft extending through thelumen, the shaft including a proximal portion and a distal portionopposite the proximal portion, the shaft and the tubular body beinglongitudinally displaceable relative to each other, wherein, when thedistal portion of the shaft is releasably coupled to the proximal regionof the leadless biostimulator, at least one of distally displacing thetubular body relative to the shaft or proximally displacing the shaftrelative to the tubular body causes the leadless biostimulator to bereceived in the volume of the atraumatic end via the distal opening andthe atraumatic end to encompass the leadless biostimulator, and at leastone of proximally displacing the tubular body relative to the shaft ordistally displacing the shaft relative to the tubular body causes theleadless biostimulator to exit the volume of the atraumatic end via thedistal opening.
 21. The delivery catheter of claim 20, wherein theatraumatic end is configured to self-bias into an increased diameterwhen the leadless biostimulator exits the volume of the atraumatic endvia the distal opening.
 22. The delivery catheter of claim 20, whereinthe atraumatic end has an internal diameter that is substantially thesame size as an outer diameter of the leadless biostimulator when theatraumatic end is in a neutral state such that the leadlessbiostimulator can be received in and removed from the volume of thetubular portion without causing any significant change to the diameterof the atraumatic end.
 23. The delivery catheter of claim 20, whereinthe at least one of a braided, woven or mesh construction includes72-144 # wires with a diameter of between approximately 0.0015 inch andapproximately 0.006 inch.
 24. A method of manufacturing a deliverycatheter, the method comprising: manufacturing an atraumatic end of thedelivery catheter by folding or rolling a cylindrical wall of a tubeback on itself to form a dual-wall construction that defines at least aportion of the atraumatic end, the tube including at least one of abraided, woven or mesh construction; and securing the atraumatic end toa distal end of a polymer tubular body of the delivery catheter.
 25. Themethod of claim 24, wherein the dual-wall construction includes an innerwall, an outer wall, a cylindrical inner volume defined by the innerwall, a folded end defining a first circular opening of the innervolume, and free ends of the inner and outer walls, the free endsdefining a second circular opening of the inner volume opposite thefirst circular opening.
 26. The method of claim 25, further comprisinglocating a sealing layer or stiffening structure between the inner andouter walls of the dual-wall construction.
 27. The method of claim 25,further comprising locating a radiopaque ring structure between theinner and outer walls of the dual-wall construction near the folded end.28. The method of claim 25, wherein the folded end is configured to havea flared or funnel configuration.
 29. The method of claim 25, furthercomprising reflowing a polymer about the free ends and then using thereflowed polymer in the securing of the atraumatic end to the tubularbody of the delivery catheter.
 30. The method of claim 25, furthercomprising locating a sealing layer about the exterior of the outer wallof the dual-wall construction.